JUKES-BROWNE : ON SOME GENERA. OF VENERID^. 237 



frequently grooved are the right posterior and the median of both right 

 and left valves. 



Gomplmia is a Western Pacific group ranging from North Australia 

 to Japan, but Liocyma is restricted to boreal seas, and may therefore be 

 regarded as the boreal representative of the former. 



2. Marcia, H. & A. Adams. 



This name was proposed by the Messrs. Adams in 1857 ^ as a sub- 

 genus of the genus Chmie, but the history of the group should begin 

 with Deshayes' " Catalogue of the Veneridse in the British Museum " 

 (1853), because Deshayes' grouping of the subdivisions of this family 

 was adopted by tlie Messrs. Adams, who only corrected and improved 

 his nomenclature. 



Deshayes had followed Gray and Megerle in recognizing Chione as 

 a distinct genus, and he subdivided it into five sections, but did not 

 give names to these, merely describing them as (1) species lamellosse, 



(2) species cancellatse, (3) species decussatse, (4) species transversim 

 striatse, (5) species laevigatse. 



The Messrs. Adams not only adopted these sections without change, 

 but furnished them with names, using such as were already in existence 

 for the four first and proposing the name Marcia for the fifth section. 

 They also gave lists of the species belonging to each of these groups, 

 following Deshayes in the main, but arranging the names in alpha- 

 betical order, so that beyond the brief diagnosis at the head they give 

 no idea of any special type. 



It is evident, therefore, that no one could form a proper conception 

 of the group for which the Messrs. Adams proposed the name Marcia 

 without being aware of the facts above mentioned, and without 

 referring to Deshayes' catalogue, where the species are not arranged 

 alphabetically ; for it is only reasonable to suppose that the first two 

 or three species of Deshayes' list are those which he had more 

 especially in view. Now the first four species in Deshaj'es' list are 

 the following: (1) Chione Kochii, Phil.; (2) C. fumigata, Sow.; 



(3) C. Ceylonensis, Sow.; (4) C. pinguis, Chem. Here, therefore, we 

 have what may be called the pinguis group, since that is the oldest 

 species, of which Ceylonensis, Sow., is merely a variety, while V. Kochii, 

 Phil., agrees with it in all essential characters, and V. fumigata, Sow. 

 (= Icevigata, Sow.), has much resemblance to the others though 

 differing a little in the teeth. Clearly, therefore, any subsequent 

 author who adopted the Messrs. Adams' name of Marcia should have 

 taken care that it included the '■^pinguis group," and should have 

 selected either pinguis or Kochii as its type. 



The first person to adopt the name Marcia seems to have been Chenu,^ 

 and, curiously enough, the only species he gives as an example is 

 V. undulom, Lam., which was certainlj^, though erroneously, placed 

 under it both by Deshayes and Messrs. Adams. 



1 Genera Receut Moll., vol. ii, p. 423. 

 - Man. Conchyl., 1862, vol. ii, p. 84. 



